A clamping apparatus, especially a machinist's vise, is known comprising a stationary clamping piece or jaw, a movable clamping piece or jaw, a clamping piston-cylinder unit with a primary piston and a secondary piston, and a hand crank drive.
In this clamping apparatus the hand crank drive has a hollow high-speed spindle and a hollow low-speed operating spindle for the clamping piston-cylinder unit located in the movable clamping piece.
The high-speed spindle is guided in a spindle nut of the stationary clamping piece. A push rod is guided in the hollow high-speed spindle. The low-speed operating spindle acts upon the hollow high-speed spindle and is guided therein. A hand crank drive engages the operating spindle. A coupling mechanism or clutch is arranged between the high-speed spindle and the operating spindle. It engages when driving the high-speed spindle and is disengaged when operating the clamping piston-cylinder unit.
In the known clamping apparatus (German published patent application No. 20 51 119) the coupling mechanism is a torque clutch of suitable structure with a loading spring and coupling components connected to each other by frictional contact. That is expensive. The torque clutch in toto is a comparatively small unit because it must be accommodated in the operating spindle. It is thus susceptible to trouble at high operating loads.